The Health Behaviour in School-aged Children (HBSC) study is a cross-national research survey conducted in collaboration with the World Health Organization (WHO) Regional Office for Europe. The HBSC aims to gain new insight into, and increase our understanding of young people's health and well-being, health behaviors and their social context. Initiated in 1982 in three countries, there are now over 35 participating countries and regions. The first cross-national survey was conducted in 1983/84, the second in 1985/86, and subsequently every four years using a common research protocol. The U.S. has been associated with the HBSC since 1993/94 and a fully participating member since 1997/98. The most recent survey was just completed for 2001/02. Besides contributing to the international survey, the U.S. simultaneously mounts a nationally representative school-based survey of ~15,000 students in grades 6-10 using identical data collection methods. Recent major studies from the 1997/98 survey have focused on the prevalence, patterns, determinants, and effects of violence, bullying behaviors, and injury, the epidemiology of depression among young adolescents, and overweight and the timing of puberty. With respect to bullying, involvement as bully, victim, or both bully and victim was assessed from nationally representative samples of 113,200 students at averages ages of 11, 13, and 15 from 25 countries, including the U.S. Involvement in bullying varied dramatically across countries, ranging from 9-54%, and was associated with poorer psychosocial adjustment. In all or nearly all countries, bullies, victims, and bully-victims reported greater health problems and poorer emotional and social adjustment. Victims and bully-victims consistently reported poorer relationships with classmates, while bullies and bully-victims reported greater alcohol use and weapon-carrying. Self-report of weapon-carrying, weapon-carrying in school, physical fighting, and being injured in a physical fight was also examined for the U.S. sample with the finding that involvement in each of the violence-related behaviors ranged from 13-23% of boys and 4-11% of girls. Greater odds of involvement occurred with bullying others than being bullied and with bullying that took place away from school than that occurring in school. The adjusted odds for weapon carrying associated with being bullied in school weekly was 1.5; for bullying others in school 2.6; for being bullied away from school 4.1; and for bullying others away from school 5.9. Thus, bullying in the U.S. is generally a marker for more serious violent behaviors, including weapon-carrying, frequent fighting, and fighting-related injury. With respect to overweight and timing of pubertal maturation, using the 1997/98 data, body mass index (BMI, kg/m2) from self-reported height and weight and the prevalence of BMI at or greater than (=>) 85th centile, and BMI => 95th centile (overweight) in 29,242 boys and girls, ages 13 and 15 years, in 15 countries and/or regions were compared. The highest prevalence of overweight was found in the U.S. and lowest in Lithuania. Based on the study reference standard, prevalence of overweight in the U.S. was 12.6% in 13-year-old boys, 10.8% in 13-year-old girls, 13.9% in 15-year-old boys, and 15.1% in 15-year-old girls, all far exceeding the 5% expected at or greater than the 95th centile. Relative rankings among countries indicated that U.S. adolescents report the highest rates of BMI => 85th centile and BMI => 95th centile (overweight) compared with European and Israeli adolescents. Follow-up studies using the 2001/02 data have looked at the timing of pubertal maturation in association with the increased body size of U.S. adolescents. In girls particularly, early maturation is associated with a higher BMI and overweight. Since other maturational patterns, especially risk-taking behavior, may also be associated with pubertal development, this relationship was investigated in the U.S. HBSC. Examples of risk behaviors examined included whether the adolescent had ever smoked tobacco or drunk alcohol to excess (got drunk). Boys' pubertal status was indicated by the appearance of hair on the upper lip (around Tanner pubic hair stage 4) and girls' by menarche (between Tanner pubic hair stages 3 and 4). At every age during peak pubertal periods, more mature adolescents were significantly taller and heavier, and the reported frequency of risk behaviors increased with age and maturational status. Adjusting for age, ethnic differences, residence and perception of family affluence, more mature boys with facial hair and post-menarcheal girls were almost twice as likely to have ever smoked or reported getting drunk. Thus, not only is the timing of pubertal maturation a factor in the development of adolescent overweight, but also in the development of risk behaviors.